Preparation of dithiooxamide



United States Patent 14 Claims. cl. zap-s51 ABSTRACT OF THE DISCLQSUREAn improvement in the preparation of dithiooxamide from hydrogen sulfideand cyanogen in the presence of a basic catalyst which involves carryingout the reaction in a liquid, substantially anhydrous and inert medium.

This invention relates to a novel method of preparing dithiooxamide,also known as rubeane and rubeanic acid, in excellent purity and yield.Dithiooxamide is a compound that is sensitive to water, rapidly turningbrown to black in aqueous suspension and even discoloring to a brownunder humid conditions. It is known to have utility as an intermediatein the preparation of pharmaceuticals and as an anti-oxidant forstabilizing ascorbic acid and petroleum products.

It is known that dithooxamide can be prepared by adding hydrogen sulfideto cyanogen as indicated by the equation:

s H S SH This reaction is accompanied by side reactions of varyingintensities depending on the reaction conditions employed, resulting indisappointingly poor yields and impurity of the desired reactionproduct.

According to Liebig and Wtihler, Annalen der Physik, vol. 24, page 167,and Volckel, Liebigs Annalen, vol. 38, pages 313-314 (1841), cyanogencan be reacted in alcoholic solution with an excess of hydrogen sulfide.V. Battista, Chem. Listy, vol. 37, page 196 (1943), suggested employingan analogous procedure using the initial materials cyanogen and hydrogensulfide in a molar ratio of 1:10, i.e., an excess of 500% hydrogensulfide, and ethanol as a solvent.

Following the instructions of the cited authors, it was found that thereaction rate and the yield are both low. For example, when the reactionis performed in 21 methanol solution, the yield of dithiooxamide is only35%. When the same reaction is performed in ether, no

dithiooxamide can be isolated. It is not surprising, therefore, thatthese methods have failed to achieve any importance in practice.

U.S. Patent 2,732,401 describes the preparation of dithiooxamide byreacting cyanogen, in an aqueous solution, with sodium hydrogen sulfide,ammonium sulfide,

ammonium sulfhydrate or various alkali and alkaline earth sulfhydrates.According to U.S. Patent 2,806,879, dithiooxamide can likewise beprepared by reacting cyanogen and hydrogen sulfide in aqueous solutionin the presence of a basic catalyst.

While these prior art suggestions gave promise of producingdithiooxamide in high yields and pure form, rendering expensivepurification steps unnecessary, actual results have left much to bedesired.

I have found that dithiooxamide is obtainable in especially pure form byreacting, at a temperature be- 3,385,890 Patented May 28, 1968 tweenabout 20 and about 100 C., preferably at l0 to 30 C., in the presence ofa basic catalyst, gaseous cyanogen with gaseous hydrogen sulfide in aliquid, substantially anhydrous (containing at most about 1% water)reaction medium, e.g. an inert organic solvent or mixture of organicsolvents for the reactants and the catalyst, until the reaction issubstantially complete. It is advantageous to employ the reactants in asubstantially stoichiometric ratio, i.e., a molar ratio of about 1:2.Either of the two reactants may be used in excess. Optimum reactionconditions are achieved when cyanogen and hydrogen sulfide areintroduced into the solvent simultaneously.

The basic catalyst suitable for use in the process of the invention mayvary widely in structure and composition. They include, by way ofexample, the cyanides, hydroxides, carbonates and lower alcoholates ofthe alkali metals, especially alkali cyanides, such as potassium cyanideand primary, secondary and tertiary amines, particularly aliphaticamines, having from 1 to 30 carbon atoms. Some of the amines that havebeen found especially suitable are, for example: n-butylamine,diethylamine, tributylamine, triethylamine, and tripropylamine. Thecatalyst concentration is not particularly crictical and may range from0.01% to 10% by weight of the reaction medium. Concentrations of theorder of about 0.5 to 3.5% by weight are preferred.

The organic solvents that are suitable for use in the process of thisinvention are those which are inert to or chemically unreactive with thereactants, the reaction product and the catalyst, capable of dissolvingthe reactants and the catalyst, and which are liquid under the reactionconditions. Solvents that are particularly suitable include aliphaticand aromatic hydrocarbons, alcohols, ethers. esters, ketones,halogenated hydrocarbons, halogenated alcohols and combinations thereof,e.g., ethyl acetate, benzene, methanol, diethyl ether, acetone andmethylene chloride. Alcohols and ketones are preferred when alkalimetal-containing catalysts are employed because of the better solubilitythereof in these solvents. Although the purity of the reaction productis excellent with :all the organic solvents tested, the yield of thereaction product varies somewhat with the solvent employed. It isparticularly advantageous to effect the addition of hydrogen sulfide todicyanogen in methanol or ethyl acetate. As shown by the data for Tests3 and 6 in the table below, dithiooxamide is obtained directly in yieldsof to and in practically pure form. The embodiments of the processillustrated in the other example are, however, also adaptable fortechnical utilization.

The advantages of the method of this invention will become furtherapparent from the following table of data summarizing the molar amountsof dicyanogen and hydrogen sulfide, the identities and amounts ofsolvents and catalysts, the reaction time (time taken to introduce thereactants simultaneously into the reaction medium) and temperature, andthe percentage of theoretical yield, analyses and appearance of thecrude dithiooxamide reaction product in each of thirteen tests. In eachtest the procedure was to stir a solution of the catalyst in the solventwhile simultaneously introducing the gaseous reactants and maintainingthe temperature specified. After the reactants had been introducedwithin the indicated period of time, stirring of the reaction mix wascontinued for one additional hour, the reaction products wassuction-filtered and dried, and the filtrate was allowed to stand for aday to observe any subsequent percipitation.

Analysis, Reactants, mol Reaction Percent percent Test Solvent G.Catalyst G.- Theor Appearance of (CN)2 H28 Tim Temp., Yield N S CrudeProduct min. C.

0.64 onion 30 -5 76.8 22.8 53.0 Orange-red. 0. 64 CHaOH 30 5 33.4 22.053.3 Do. 4.48 0113011 210 -5 100 23.3 D0. 1.23 CI'IBOH 60 to 13 32.523.0 53.3 Do. 1.103 OHZO 00 15 to 13 91.5 22.9 53.6 Red-brown. 0.64 CHaC30 5 to 10 95.3 23.2 Orange-red. 0.04 OH3GOOC2H5- 99 30 10 to 10 33.523.4 Do. 0. 64 0113000113 00 30 3 to s 62.3 23.3 Light Orange. 0. 64011.01. 99 30 3 to s 62.8 23.6 Do. 0.64 30 10 to 16 33.3 23.3 Do. 1.1860 11 to 16 78.8 22.3 Light Brown. 0. 64 1 30 10 to 16 51.6 22.8 Brown.0.64 OzHmN 1 30 10 to 10 65.3 22.1 Light Brown.

1 Theoretical.

No subsequent precipitation was observable in any 7. A process asdefined in claim 1 wherein the organic of Tests 1 to 11, summarizedabove. In Tests 12 and 13, solvent is methylene chloride. however, 7.5and 4.7 grams, respectively, of subsequent 20 8. A process as defined inclaim 1 wherein the organic precipitate were found. Theafter-precipitate of Test 12 solvent is benzene. was a black substancehaving a nitrogen content of 9. A process as defined in claim 1 whereinthe catalyst 14.85%, and that of Test 13 was a sticky, brown-black ispotassium cyanide. mass having a nitrogen content of 21.7% 10. A processas defined in claim 1 wherein the catalyst I claim: is diethylamine. 1.A process for preparing dithiooxamide which com- 11. A process asdefined in claim 1 wherein the catalyst prises introducing gaseouscyanogen and hydrogen sulis n-butylamine. fide into an inert, liquid,substantially anhydrous organic 12. A process as defined in claim 1wherein the catalyst solvent containing between about 0.01% and about10% is triethylamine. by weight, based on the weight of the reactionmedium, 13. A process as defined in claim 1 wherein the molar of a basiccatalyst while maintaining the reaction medium ratio of cyanogen tohydrogen sulfide is about 1:2. at a temperature between about 20 andabout 100 C. 14. A process as defined in claim 1 wherein the cyan- 2. Aprocess as defined in claim 1 wherein the tem ogen and hydrogen sulfideare introduced simultaneously perature is maintained at between 10 and+30 C. into the reaction medium.

3. A process as defined in claim 1 wherein the reaction medium containsbetween about 0.5 and 3.5% by References Cited i y d fi d 1 1 h h UNITEDSTATES PATENTS process as e me me am W ereint e organic solvent ismethanol. 2,806,879 9/1957 Kaiser et a1. 260551 5. A process as definedin claim 1 wherein the organic solvent is ethyl acetate.

6. A process as defined in claim 1 wherein the organic solvent isacetone.

CHARLES E. PARKER, Primary Examiner. R. HINES, Assistant Examiner.

